DUPLEX Efficacy Results: Proteinuria Remission Beyond the Primary Endpoint

In "DUPLEX Efficacy Results: Proteinuria Remission Beyond the Primary Endpoint," our experts turn to the efficacy results behind sparsentan's approval, and why a missed primary endpoint didn't tell the whole story.

Dr. Campbell walks through the DUPLEX efficacy results, starting with the disappointing headline: at the week 108 final analysis, the between-group difference in eGFR slope wasn't statistically significant. But he highlights that the secondary endpoint, total GFR change from baseline to week 112, did show benefit, with sparsentan patients declining 10.4 mL/min/year compared to 12.0 for irbesartan, a 1.8 mL/min/year advantage. The proteinuria data proved more striking: sparsentan produced a 50% mean UPCR reduction versus 32% for irbesartan, with 37.5% of sparsentan patients reaching classic partial remission compared to 22.6% on irbesartan. Time to first partial remission was 14.1 weeks with sparsentan versus 109 weeks with irbesartan, and complete remission was reached by 18.5% versus roughly 7%. Post-hoc analysis showed that, regardless of treatment arm, achieving remission tracked with reduced progression to kidney failure.

Dr. Trachtman argues the primary endpoint's failure was effectively hardwired into FSGS's biological variability rather than a true drug failure, noting that panicked journal-club reactions calling the trial a bust missed that the proteinuria signal carries real long-term meaning. He explains the FDA's underlying logic: the agency traditionally treats GFR as the hard outcome tied to survival and function, but DUPLEX forced regulators to weigh whether GFR was even a realistic FSGS trial endpoint given the disease's urgent unmet need and a compelling proteinuria signal. Dr. Trachtman also connects the faster remission timeline to clinical counseling, noting that where calcineurin inhibitors often require three to six months to judge, sparsentan's two-to-three-month signal lets clinicians reassure patients earlier that treatment is working and worth continuing, strengthening the case for staying on therapy.

The next episode in this series, "Sparsentan Safety and the REMS Monitoring Requirement in FSGS," shifts to the safety data and the monitoring program clinicians will need to navigate.